Synthesis of alpha-galactosyl ceramide, a potent immunostimulatory agent

Strategies for targeted gene delivery using lipid nanoparticles and cell-derived nanovesicles

Gene therapy is a promising approach for the treatment of many diseases. However, the effective delivery of the cargo without degradation in vivo is one of the major hurdles. With the advent of lipid nanoparticles (LNPs) and cell-derived nanovesicles (CDNs), gene delivery holds a very promising future. The targeting of these nanosystems is a prerequisite for effective transfection with minimal side-effects. In this review, we highlight the emerging strategies utilized for the effective targeting of LNPs and CDNs, and we summarize the preparation methodologies for LNPs and CDNs. We have also highlighted the non-ligand targeting of LNPs toward certain organs based on their composition. It is highly expected that continuing the developments in the targeting approaches of LNPs and CDNs for the delivery system will further promote them in clinical translation.

Characterization of a Glycolipid Synthase Producing α-Galactosylceramide in Bacteroides fragilis

Glycolipids are complex molecules involved in important cellular processes. Among them, the glycosphingolipid α-galactosylceramide has proven to be of interest in biomedicine for its immunostimulatory capabilities. Given its structural requirements, the use of ceramide glycosyltransferase enzymes capable of synthesizing this molecule under in vivo or in vitro conditions is a potential production strategy. Several GT4 enzymes from Bacteroides fragilis were considered as potential candidates in addition to the known BF9343_3149, but only this one showed glycolipid synthase activity. The enzyme was expressed as a SUMO fusion protein to produce soluble protein. It is a non-processive glycosyltransferase that prefers UDP-Gal over UDP-Glc as a donor substrate, and maximum activity was found at pH 7.3 and around 30-35 °C. It does not require metal cations for activity as other GT4 enzymes, but Zn²⁺ inactivates the enzyme. The reaction occurs when the ceramide lipid acceptor is solubilized with BSA (100% conversion) but not when it is presented in mixed micelles, and anionic lipids do not increase activity, as in other membrane-associated glycolipid synthases. Further protein engineering to increase stability and activity can make feasible the enzymatic synthesis of α-GalCer for biomedical applications.

Diversity-Oriented Synthesis of a Molecular Library of Immunomodulatory α-Galactosylceramides with Fluorous-Tag-Assisted Purification and Evaluation of Their Bioactivities in Regard to IL-2 Secretion

Structural variants of α-galactosylceramide (α-GalCer) that stimulate invariant natural killer T (iNKT) cells constitute an emerging class of immunomodulatory agents in development for numerous biological applications. Variations in lipid chain length and/or fatty acids in these glycoceramides selectively trigger specific pro-inflammatory responses. Studies that would link a specific function to a structurally distinct α-GalCer rely heavily on the availability of homogeneous and pure materials. To address this need, we report herein a general route to the diversification of the ceramide portion of α-GalCer glycolipids. Our convergent synthesis commences from common building blocks and relies on the Julia–Kocienski olefination as a key step. A cleavable fluorous tag is introduced at the non-reducing end of the sugar that facilitates quick purification of products by standard fluorous solid-phase extraction. The strategy enabled the rapid generation of a focused library of 61 α-GalCer analogs by efficiently assembling various lipids and fatty acids. Furthermore, when compared against parent α-GalCer in murine cells, many of these glycolipid variants were found to have iNKT cell stimulating activity similar to or greater than KRN7000. ELISA assaying indicated that glycolipids carrying short fatty N-acyl chains (1fc and 1ga), an unsubstituted (1fh and 1fi) or CF3-substituted phenyl ring at the lipid tail, and a flexible, shorter fatty acyl chain with an aromatic ring (1ge, 1gf, and 1gg) strongly affected the activation of iNKT cells by the glycolipid-loaded antigen-presenting molecule, CD1d. This indicates that the method may benefit the design of structural modifications to potent iNKT cell-binding glycolipids.

Potent Neutralizing Antibodies Elicited by RBD-Fc-Based COVID-19 Vaccine Candidate Adjuvanted by the Th2-Skewing iNKT Cell Agonist

The development of a safe and effective COVID-19 vaccine is of paramount importance to terminate the current pandemic. An adjuvant is crucial for improving the efficacy of the subunit COVID19 vaccine. α-Galactosylceramide (αGC) is a classical iNKT cell agonist which causes the rapid production of Th1- and Th2-associated cytokines; we, therefore, expect that the Th1- or Th2-skewing analogues of αGC can better enhance the immunogenicity of the receptor-binding domain in the spike protein of SARS-CoV-2 fused with the Fc region of human IgG (RBD-Fc). Herein, we developed a universal synthetic route to the Th1-biasing (α-C-GC) and Th2-biasing (OCH and C20:2) analogues. Immunization of mice demonstrated that αGC-adjuvanted RBD-Fc elicited a more potent humoral response than that observed with Alum and enabled the sparing of antigens. Remarkably, at a low dose of the RBD-Fc protein (2 μg), the Th2-biasing agonist C20:2 induced a significantly higher titer of the neutralizing antibody than that of Alum.

In-Depth Structural Characterization and Quantification of Cerebrosides and Glycosphingosines with Gas-Phase Ion Chemistry

Cerebrosides (n-HexCer) and glycosphingosines (n-HexSph) constitute two sphingolipid subclasses. Both are comprised of a monosaccharide headgroup (glucose or galactose in mammalian cells) linked via either an α- or β-glycosidic linkage to the sphingoid backbone (n = α or β, depending upon the nature of the linkage to the anomeric carbon of the sugar). Cerebrosides have an additional amide-bonded fatty acyl chain linked to the sphingoid backbone. While differentiating the multiple isomers (i.e. glucose vs galactose, α- vs β-linkage) is difficult, it is crucial for understanding their specific biological roles in health and disease states. Shotgun tandem mass spectrometry has been a powerful tool in both lipidomics and glycomics analysis but is often limited in its ability to distinguish isomeric species. This work describes a new strategy combining shotgun tandem mass spectrometry with gas-phase ion chemistry to achieve both differentiation and quantification of isomeric cerebrosides and glycosphingosines. Briefly, deprotonated cerebrosides, [n-HexCer-H]^-, or glycosphingosines, [n-HexSph-H]^-, are reacted with terpyridine (Terpy) magnesium complex dications, [Mg(Terpy)₂]²⁺, in the gas phase to produce a charge-inverted complex cation, [n-HexCer-H+MgTerpy]⁺ or [n-HexSph-H+MgTerpy]⁺. The collision-induced dissociation (CID) of the charge-inverted complex cations leads to significant spectral differences between the two groups of isomers, α-GalCer, β-GlcCer, and β-GalCer for cerebrosides and α-GlcSph, α-GalSph, β-GlcSph, and β-GalSph for glycosphingosines, which allows for isomer distinction. Moreover, we describe a quantification strategy with the normalized percent area extracted from selected diagnostic ions that quantify either three isomeric cerebroside or four isomeric glycosphingosine mixtures. The analytical performance was also evaluated in terms of accuracy, repeatability, and interday precision. Furthermore, CID of the product ions resulting from 443 Da loss from the charge-inverted complex cations ([n-HexCer-H+MgTerpy]⁺) has been performed and demonstrated for localization of the double-bond position on the amide-bonded monounsaturated fatty acyl chain in the cerebroside structure. The proposed strategy was successfully applied to the analysis of total cerebroside extracts from the porcine brain, providing in-depth structural information on cerebrosides from a biological mixture.

Broadening the Message: A Nanovaccine Co-loaded with Messenger RNA and α-GalCer Induces Antitumor Immunity through Conventional and Natural Killer T Cells

Messenger RNA encoding tumor antigens has the potential to evoke effective antitumor immunity. This study reports on a nanoparticle platform, named mRNA Galsomes, that successfully co-delivers nucleoside-modified antigen-encoding mRNA and the glycolipid antigen and immunopotentiator α-galactosylceramide (α-GC) to antigen-presenting cells after intravenous administration. By co-formulating low doses of α-GC, mRNA Galsomes induce a pluripotent innate and adaptive tumor-specific immune response in mice, with invariant natural killer T cells (iNKT) as a driving force. In comparison, mRNA Galsomes exhibit advantages over the state-of-the-art cancer vaccines using unmodified ovalbumin (OVA)-encoding mRNA, as we observed up to seven times more tumor-infiltrating antigen-specific cytotoxic T cells, combined with a strong iNKT cell and NK cell activation. In addition, the presence of suppressive myeloid cells (myeloid-derived suppressor cells and tumor-associated macrophages) in the tumor microenvironment was significantly lowered. Owing to these antitumor effects, OVA mRNA Galsomes significantly reduced tumor growth in established E.G7-OVA lymphoma, with a complete tumor rejection in 40% of the animals. Moreover, therapeutic vaccination with mRNA Galsomes enhanced the responsiveness to treatment with a PD-L1 checkpoint inhibitor in B16-OVA melanoma, as evidenced by a synergistic reduction of tumor outgrowth and a significantly prolonged median survival. Taken together, these data show that intravenously administered mRNA Galsomes can provide controllable, multifaceted, and effective antitumor immunity, especially when combined with checkpoint inhibition.

4"-O-Alkylated α-Galactosylceramide Analogues as iNKT-Cell Antigens: Synthetic, Biological, and Structural Studies

Invariant natural killer T-cells (iNKT) are a glycolipid-responsive subset of T-lymphocytes that fulfill a pivotal role in the immune system. The archetypical synthetic glycolipid, α-galactosylceramide (α-GalCer), whose molecular framework is inspired by a group of amphiphilic natural products, remains the most studied antigen for iNKT-cells. Nonetheless, the potential of α-GalCer as an immunostimulating agent is compromised by the fact that this glycolipid elicits simultaneous secretion of Th1- and Th2-cytokines. This has incited medicinal chemistry efforts to identify analogues that are able to perturb the Th1/Th2 balance. In this work, we present the synthesis of an extensive set of 4"-O-alkylated α-GalCer analogues, which were evaluated in vivo for their cytokine induction. We have found that conversion of the 4"-OH group to ether moieties decreases the immunogenic potential in mice relative to α-GalCer. Yet, the benzyl-modified glycolipids are able to produce a distinct pro-inflammatory immune response. The crystal structures suggest an extra hydrophobic interaction between the benzyl moiety and the α2-helix of CD1d.

Fourier Transform Mass Spectrometry and Nuclear Magnetic Resonance Analysis for the Rapid and Accurate Characterization of Hexacosanoylceramide

Ceramides are a central unit of all sphingolipids which have been identified as sites of biological recognition on cellular membranes mediating cell growth and differentiation. Several glycosphingolipids have been isolated, displaying immunomodulatory and anti-tumor activities. These molecules have generated considerable interest as potential vaccine adjuvants in humans. Accurate analyses of these and related sphingosine analogues are important for the characterization of structure, biological function, and metabolism. We report the complementary use of direct laser desorption ionization (DLDI), sheath flow electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) and high-field nuclear magnetic resonance (NMR) analysis for the rapid, accurate identification of hexacosanoylceramide and starting materials. DLDI does not require stringent sample preparation and yields representative ions. Sheath-flow ESI yields ions of the product and byproducts and was significantly better than monospray ESI due to improved compound solubility. Negative ion sheath flow ESI provided data of starting materials and products all in one acquisition as hexacosanoic acid does not ionize efficiently when ceramides are present. NMR provided characterization of these lipid molecules complementing the results obtained from MS analyses. NMR data was able to differentiate straight chain versus branched chain alkyl groups not easily obtained from mass spectrometry.

Illuminating the binding interactions of galactonoamidines during the inhibition of β-galactosidase (E. coli)

Several galactonoamidines were previously identified as very potent competitive inhibitors that exhibit stabilizing hydrophobic interactions of the aglycon in the active site of β-galactosidase (Aspergillus oryzae). To elucidate the contributions of the glycon to the overall inhibition ability of the compounds, three glyconoamidine derivatives with alteration in the glycon at C-2 and C-4 were synthesized and evaluated herein. All amidines are competitive inhibitors of β-galactosidase (Escherichia coli) and show significantly reduced inhibition ability when compared to the parent. The results highlight strong hydrogen-bonding interactions between the hydroxyl group at C-2 of the amidine glycon and the active site of the enzyme. Slightly weaker H-bonds are promoted through the hydroxyl group at C-4. The inhibition constants were determined to be picomolar for the parent galactonoamidine, and nanomolar for the designed derivatives rendering all glyconoamidines very potent inhibitors of glycosidases albeit the derivatized amidines show up to 700-fold lower inhibition activity than the parent.

Synthesis and Activity of 6″-Deoxy-6″-thio-α-GalCer and Peptide Conjugates

A major challenge in the development of highly defined synthetic vaccines is the codelivery of vaccine components (i.e., antigen and adjuvant) to secondary lymphoid tissue to induce optimal immune responses. This problem can be addressed by synthesizing vaccines that comprise peptide antigens covalently attached to glycolipid adjuvants through biologically cleavable linkers. Toward this, a strategy utilizing previously unreported 6″-deoxy-6″-thio analogues of α-GalCer that can undergo chemoselective conjugation with peptide antigens is described. Administration of these conjugate vaccines leads to enhanced priming of antigen specific T cells. This simple vaccine design is broadly applicable to multiple disease indications such as cancer and infectious disease.

An autologous leukemia cell vaccine prevents murine acute leukemia relapse after cytarabine treatment

Acute leukemias with adverse prognostic features carry a high relapse rate without allogeneic stem cell transplantation (allo-SCT). Allo-SCT has a high morbidity and is precluded for many patients because of advanced age or comorbidities. Postremission therapies with reduced toxicities are urgently needed. The murine acute leukemia model C1498 was used to study the efficacy of an intravenously administered vaccine consisting of irradiated leukemia cells loaded with the natural killer T (NKT)-cell agonist α-galactosylceramide (α-GalCer). Prophylactically, the vaccine was highly effective at preventing leukemia development through the downstream activities of activated NKT cells, which were dependent on splenic langerin(+)CD8α(+) dendritic cells and which led to stimulation of antileukemia CD4(+) and CD8(+) T cells. However, hosts with established leukemia received no protective benefit from the vaccine, despite inducing NKT-cell activation. Established leukemia was associated with increases in regulatory T cells and myeloid-derived suppressor cells, and the leukemic cells themselves were highly suppressive in vitro. Although this suppressive environment impaired both effector arms of the immune response, CD4(+) T-cell responses were more severely affected. When cytarabine chemotherapy was administered prior to vaccination, all animals in remission posttherapy were protected against rechallenge with viable leukemia cells.

Synthesis of α-L-rhamnosyl ceramide and evaluation of its binding with anti-rhamnose antibodies

An α-L-rhamnosyl ceramide (1, α-L-RhaCer) has been prepared that was recognized by anti-L-rhamnose (anti-Rha) antibodies. During these studies we explored the use of an α-L-rhamnosyl thioglycoside and a trichloroacetimidate as a glycosyl donors. Subsequently, the acceptors desired for glycosylation, 3-O-benzoylazidosphingosine or 3-O-alloxycarbonylsphingosine, were prepared from D-xylose. The thioglycoside donor, 2,3,4-tri-O-acetyl-1-(4-tolyl)thio-α-L-rhamnopyranoside, and the trichloroacetimidate donor, 2,3,4-tri-O-acetyl-1-(2,2,2-trichloroethanimidate)-α-L-rhamnopyranoside, were synthesized in 50% and 78% yield overall, respectively. The synthesis of the glycosylation acceptor employed an addition-fragmentation olefination that was successfully carried out in 53% yield. With the successful synthesis of key intermediates, α-L-RhaCer (1) was prepared without any insurmountable obstacles. Anti-Rha antibodies were prepared in BALB/c mice by immunizing them with rhamnose-ovalbumin (Rha-Ova) with Sigma Adjuvant System (SAS) and the anti-L-Rha antibodies were isolated from the blood sera. Liposomes and EL4 tumor cells were used as model systems to demonstrate the ability of 1 to insert into a lipid bilayer. The interaction of the liposomes or the EL4 cells with α-L-RhaCer (1) and anti-Rha antibodies were investigated by fluorescence microscopy and flow cytometry, respectively, to confirm the ability of glycolipid 1 to be displayed on the tumor cell surface as well as the ability to be recognized by anti-Rha antibodies.

Total synthesis of the Escherichia coli O111 O-specific polysaccharide repeating unit

The first total synthesis of the O-antigen pentasaccharide repeating unit from Gram-negative bacteria Escherichia coli O111 was achieved starting from four monosaccharide building blocks. Key to the synthetic approach was a bis-glycosylation reaction to combine trisaccharide 10 and colitose 5. The colitose building block (5) was obtained de novo from non-carbohydrate precursors. The pentasaccharide was equipped at the reducing end with an amino spacer to provide a handle for subsequent conjugation to a carrier protein in anticipation of immunological studies.

Synthesis and evaluation of acyl-chain- and galactose-6''-modified analogues of α-GalCer for NKT cell activation

α-GalCer is an immunostimulating glycolipid that binds to CD1d molecules and activates invariant natural killer T (iNKT) cells. Here we report a scaled-up synthesis of α-GalCer analogues with modifications in the acyl side chain and/or at the galactose 6''-position, together with their evaluation in vitro and in vivo. Analogues containing 11-phenylundecanoyl acyl side chains with aromatic substitutions (14, 16-21) and Gal-6''-phenylacetamide-substituted α-GalCer analogues bearing p-nitro- (32), p-tert-butyl (34), or o-, m-, or p-methyl groups (40-42) displayed higher IFN-γ/IL-4 secretion ratios than α-GalCer in vitro. In mice, compound 16, with an 11-(3,4-difluorophenyl)undecanoyl acyl chain, induced significant proliferation of NK and DC cells, which should be beneficial in killing tumors and priming the immune response. These new glycolipids might prove useful as adjuvants or anticancer agents.

Structure-activity relationship studies of novel glycosphingolipids that stimulate natural killer T-cells

KRN7000, an anticancer drug candidate developed by Kirin Brewery Co. in 1995, is an α-galactosyl ceramide. It is a ligand making a complex with CD1d protein, and it stimulates invariant natural killer T (NKT) cells, which are one of the lineages of immunocytes. NKT cells activated by recognition of the CD1d/KRN7000 complex with its invariant T-cell receptor (TCR) can induce both protective and regulatory immune responses. To determine the recognition and activation mechanisms of NKT cells and to develop drug candidates more effective than KRN7000, a large number of analogs of KRN7000 have been synthesized. Some of them show potent bioactivities and have the potential of being utilized as therapeutic agents. In this review, structure-activity relationship studies of novel glycolipids which stimulate NKT cells efficiently are summarized.

Species-specific activity of glycolipid ligands for invariant NKT cells

The immunomodulatory glycolipid α-galactosylceramide (α-GalCer) binds to CD1d and exhibits potent activity as a ligand for invariant CD1d-restricted natural killer-like T cells (iNKT cells). Structural analogues of α-GalCer have been synthesised to determine which components are required for CD1d presentation and iNKT cell activation, however, to date the importance of the phytosphingosine 4-hydroxyl for iNKT cell activation has been disputed. To clarify this, we synthesised two 4-deoxy α-GalCer analogues (sphinganine and sphingosine) and investigated their ability to activate murine and human iNKT cells. Analysis revealed that the analogues possessed comparable activity to α-GalCer in stimulating murine iNKT cells, but were severely compromised in their ability to stimulate human iNKT cells. Here we determined that species-specific glycolipid activity was due to a lack of recognition of the analogues by the T-cell receptors on human iNKT cells rather than insufficient presentation of the analogues on human CD1d molecules. From these results we suggest that glycolipids developed for potent iNKT cell activity in humans should contain a phytosphingosine base.

Synthesis of amino core compounds of galactosyl phytosyl ceramide analogs for developing iNKT-cell inducers

1-Aminophytosphingosine and 6-aminogalactosyl phytosphingosine were prepared in 61% and 40% yield libraries with 44 carboxylic acids showed that a 4-butylbenzoic acid-derived product exe, respectively. Glycosylation using benzoyl-protected lipid resulted in better a-selectivity for ceramide analogs, but the yield was less than that obtained with benzyl moieties. Screening the amide rted less cytotoxicity. These analogs were purified for validation of immunological potencies and the a-GalCer analog but not the sphingosine analog stimulated human iNKT cell population.

Divergent synthetic approach to 6''-modified α-GalCer analogues

A synthetic approach is presented for the synthesis of galacturonic acid and D-fucosyl modified KRN7000. The approach allows for late-stage functionalisation of both the sugar 6''-OH and the sphingosine amino groups, which enables convenient synthesis of promising 6''-modified KRN7000 analogues.

Endogenous and Exogenous CD1-Binding Glycolipids

In the same way that peptide antigens are presented by major histocompatibility complex (MHC) molecules, glycolipid antigens can also activate the immune response via binding to CD1 proteins on antigen-presenting cells (APCs) and stimulate CD1-restricted T cells. In humans, there are five members of the CD1 family, termed CD1a–e, of which CD1a–d are involved in glycolipid presentation at the cell surface, while CD1e is involved in the intracellular trafficking of glycolipid antigens. Both endogenous (self-derived) and exogenous (non-self-derived) glycolipids have been shown to bind to members of the CD1 family with varying degrees of specificity. In this paper we focus on the key glycolipids that bind to the different members of the CD1 family.

A general and concise asymmetric synthesis of sphingosine, safingol and phytosphingosines via tethered aminohydroxylation

A novel, practical and efficient enantioselective synthesis of sphingoid bases, l-threo-[2S,3S]-sphinganine (safingol), l-threo-[2S,3S]-sphingosine, l-arabino-[2R,3S,4R] and l-xylo-[2R,3S,4S]-C(18)-phytosphingosine is described. The synthetic strategy features the Sharpless kinetic resolution and tethered aminohydroxylation (TA) as the key steps.

Synthesis of truncated analogues of the iNKT cell agonist, α-galactosyl ceramide (KRN7000), and their biological evaluation

Stimulation of iNKT cells by α-galactosyl ceramide (α-GalCer), also known as KRN7000, and its truncated analogue OCH induces both Th1- and Th2-cytokines, with OCH inducing a Th2-cytokine bias. Skewing of the iNKT cells’ response towards either a Th1- or Th2-cytokine profile offers potential therapeutic benefits. The length of both the acyl and the sphingosine chains in α-galactosyl ceramides is known to influence the cytokine release profile. We have synthesized analogues of α-GalCer with truncated sphingosine chains for biological evaluation, with particular emphasis on the Th1/Th2 distribution. Starting from a common precursor, d-lyxose, the sphingosine derivatives were synthesised via a straightforward Wittig condensation.

Synthesis and evaluation of amino-modified alpha-GalCer analogues

Alpha-GalCer analogues featuring a phytoceramide 3- and 4-amino group have been synthesized. A Mitsunobu reaction involving phthalimide was employed for the introduction of the amino groups at the 3- and 4-positions of suitable phytosphingosine-derived precursors. The influence of these modifications on the interaction with the T-cell receptor of NKT cells was investigated, as well as the capacity of the amino-modified analogues to induce a cytokine response after in vivo administration.

Novel galactosyl donor with 2-naphthylmethyl (NAP) as the non participating group at C-2 position: Efficient synthesis of alpha-galactosyl ceramide

Predominant alpha-linked products can be generated in glycosylation involving galactosyl trichloroacetimidate donors with 2-naphthylmethyl (NAP) as the non participating group at C-2 position. The above donor was successfully utilized for the synthesis of alpha-galactosyl ceramide.

Efficient synthesis of galactosylceramide analogues for iNKT cell stimulation

Glycolipids are potential antigens for iNKT cells recognition and demonstrate important roles in both innate and adaptive immunity. However, the difficulties in the preparation of pure configuration defined glycolipids limit the exploration of their different profiles in activating iNKT cells. We report here a concise and stereospecific preparation of novel galactosylceramide analogues by oxime ligation. This strategy would provide an efficient way to generate varied glycolipid analogues with either synthetic or natural carbohydrates for biological evaluations.

Synthesis and biological activity of ester and ether analogues of alpha-galactosylceramide (KRN7000)

Alpha-Galactosylceramide (alphaGalCer, KRN7000) has been identified as a modulator of immunological processes through its capacity to bind iNKT cells mediated by CD1d molecules. Some analogues in while the amide group in alphaGalCer is replaced with ester or ether groups were synthesized from d-arabinitol or l-ribose to evaluate their ability to activate iNKT cells. Ester analogues 30a, 31a, and 61 showed activity for IFNgamma and IL-4 production of iNKT cells, while ether (31b) and 4-methoxy ester (76) analogues of alpha-galactosylceramide were not active for iNKT cells.

Sensitive and specific enzyme immunoassays for antigenic trisaccharide from Bacillus anthracis spores

A straightforward synthesis of an anthrose-containing trisaccharide derived from Bacillus anthracis was achieved. Antibodies raised against this hapten provide a highly sensitive enzyme immunoassay with a detection limit of 8.5 pmol mL(-1). By investigating the specificity of the antibodies obtained using different mono-, di- and trisaccharide synthetic analogues, we demonstrated that the epitope was mainly made up of the methyl group at C-5, the butamido group at C-4 and the hydroxyl at C-3 of the anthrose unit, the other parts of the trisaccharide appearing little involved in the recognition.

The synthesis and in vivo evaluation of 2',2'-difluoro KRN7000

The synthesis of 2',2'-difluoro KRN7000 is described. In vivo evaluation demonstrates that this fluorinated glycolipid induces CD1d-dependent TCR activation of NKT cells, with a bias towards Th2 cytokine production.

Synthesis and evaluation of sphingolipid analogues: modification of the hydroxy group at C(1) of 7-oxasphingosine, and of the hydroxy group at C(1) and the amide group of 7-oxaceramides

The analogues 7-9 of 7-oxaceramide and 7-oxasphingosine were synthesized from the known azidosphingosine 21. The 1,4-disubstituted 1,2,3-triazole analogues 10-16 of ceramides were synthesized by the click reaction of the known azide 24. None of the analogues 7-15 was active as inhibitor of SPHK type 1 and of acid sphingomyelinase, whereas 16 is a weak inhibitor of SPHK1. Triazoles 10, 11, and 15 did not inhibit ceramide phosphorylation by CerK, and none of 7, 8, and 10-15 activated invariant natural killer T (iNKT) cell clones when presented by human CD1d-transfected antigen-presenting cells (APC) or by plate-bound human CD1d [55]. Triazoles 14 and 15 prevent binding of alpha-galactosylceramide (alpha-GalCer) to plate-bound human CD1d and subsequent T-cell response to alpha-GalCer. Only 15 reduced activation by alpha-GalCer significantly and independently of the cytokine measured.

Glycosyl iodides. History and recent advances

The use of glycosyl iodides as an effective method for the preparation of glycosides has had a recent resurgence in carbohydrate chemistry, despite its early roots in which these species were believed to be of limited use. Renewed interest in these species as glycosylating agents has been spurred by their demonstrated utility in the stereoselective preparation of O-glycosides, and other glycosylic compounds. This review provides a brief historical account followed by an examination of the use of glycosyl iodides in the synthesis of oligosaccharides and other glycomimetics, including C-glycosylic compounds, glycosyl azides and N-glycosides.

An efficient and general enantioselective synthesis of sphingosine, phythosphingosine, and 4-substituted derivatives

A general and efficient protocol for the enantioselective synthesis of sphingosine, phythosphingosine, and 4-substituted derivatives was established. These compounds were obtained from a common intermediate prepared from butadiene monoepoxide by a synthetic sequence involving enantioselective allylic substitution, cross-metathesis, and dihydroxylation.